As dynamic random access memory (DRAM) devices become more highly integrated, the area available for each memory cell is reduced. Accordingly, the substrate area available for each memory cell capacitor may be reduced so that it may be difficult to maintain a desired memory cell capacitance as integration densities increase. Reduced memory cell capacitances may increase a soft error rate (SER), degrade memory cell operation at low voltages, and/or result in more frequent memory refresh operations. Accordingly, there exists a need to provide a memory cell capacitor occupying a reduced surface area of the memory device substrate while maintaining a desired capacitance.
In response, capacitors having three-dimensional structures have been proposed to increase the surface area of the capacitor electrodes thereby increasing the capacitance of the resulting capacitor. In particular, cylindrical electrode structures may be used where inner and outer surfaces of a cylinder are used to increase an effective capacitor electrode area. A surface area of a cylindrical capacitor electrode structure may be further increased by increasing a height of the structure.
A cylindrical electrode structure may be formed, for example, as shown in FIGS. 6A-B. As shown in FIG. 6A, an insulating layer 701 and an etch stopping layer 703 may be formed on a substrate 700, and conductive plugs 702 may provide electrical coupling through the etch stopping and insulating layers 703 and 701. A first sacrificial layer 704 may be formed on the etch stopping layer 703, and holes through the first sacrificial layer 704 may expose the conductive plugs 702. Cylindrical electrodes 705 may be formed on sidewalls of the holes in the first sacrificial layer 704, and a second sacrificial layer 706 may be provided within the cylindrical electrodes.
The sacrificial layers 704 and 706 may be removed as shown in FIG. 6B so that inside and outside surfaces of the cylindrical electrodes 705 are exposed, and a capacitor dielectric layer and a second capacitor electrode may be formed on the exposed surfaces of the cylindrical electrodes 705. With relatively tall and/or closely packed cylindrical electrode structures, however, adjacent cylindrical electrodes may lean together once the support provided by the sacrificial layers is removed. As shown in FIG. 6B, an electrical short may thus result between adjacent cylindrical electrodes at 707 prior to forming a capacitor dielectric layer. For example, cylindrical electrodes may lean together while being cleaned and/or dried after removing the sacrificial layers.